CQI report
UE sends a Channel Quality Indicator (CQI) on the uplink (HS-DPCCH)CQI
-Estimates the number of bits that can be transmitted to the UE using a certain assumed HS-PDSCH -power with a block error rate of 10%-UE receiver performance
Good UE receiver can report that it can receive more bits than a Bad UE receiver implementation for the same channel conditions.
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PCPICH_RX
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Received power of the P-CPICH
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Г
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Measurement Power Offset MPO
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Cell level parameter hsMeasurementPowerOffset
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∆
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Reference power adjustment
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Given by Table 7A, 7B, 7C, 7D, 7E, 7F or 7G depending on
the UE category.
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Physical layer procedures (FDD)
CQI algorithm indicates
-Transport block size
-Number of HS-PDSCH codes
-Modulation Type
-HS-PDSCH Power
HSDPA Scheduler algorithm indicates
-Which UE to transmit to in the TTI,
-Available HS-PDSCH transmission power, Available number of HS-PDSCH codes.
-It does not indicate how much data to transmit.
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CAT6
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||||
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CQI Value
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Transport Block Size
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Number of HS-PDSCH
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Modulation
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Reference Power Adjustment
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1
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137
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1
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QPSK
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0
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2
|
173
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1
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QPSK
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0
|
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3
|
233
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1
|
QPSK
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0
|
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4
|
317
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1
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QPSK
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0
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5
|
377
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1
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QPSK
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0
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6
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461
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1
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QPSK
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0
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7
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650
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2
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QPSK
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0
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8
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792
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2
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QPSK
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0
|
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9
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931
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2
|
QPSK
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0
|
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10
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1262
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3
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QPSK
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0
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11
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1483
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3
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QPSK
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0
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12
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1742
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3
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QPSK
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0
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13
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2279
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4
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QPSK
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0
|
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14
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2583
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4
|
QPSK
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0
|
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15
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3319
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5
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QPSK
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0
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16
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3565
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5
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16-QAM
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0
|
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17
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4189
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5
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16-QAM
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0
|
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18
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4664
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5
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16-QAM
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0
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19
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5287
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5
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16-QAM
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0
|
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20
|
5887
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5
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16-QAM
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0
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21
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6554
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5
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16-QAM
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0
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22
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7168
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5
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16-QAM
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0
|
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23
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7168
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5
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16-QAM
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-1
|
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24
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7168
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5
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16-QAM
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-2
|
|
25
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7168
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5
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16-QAM
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-3
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26
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7168
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5
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16-QAM
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-4
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27
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7168
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5
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16-QAM
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-5
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28
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7168
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5
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16-QAM
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-6
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|
29
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7168
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5
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16-QAM
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-7
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|
30
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7168
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5
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16-QAM
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-8
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Why CQI?
Back to Basics:
PN codes (distinguish each Base Station)
-Not orthogonal
-High cross correlation properties
-PN1 * PN2 ≠ 0 (mini. output)
Channelization Codes (distinguish data channels Coming from each Base Station)
-Orthogonal Codes
-OC1 * OC2 = 0
-Ec/No for most of us is quality measurement metric.
-It gives us how good or bad the link quality is.
-However by definition it is confusing
RSCP
-Received signal code power
-Received power level of pilot channel of a one cell (dBm/mW)
-Using RSCP we can compare different cells
-Using RSCP handover and cell reselection decisions can be taken
RSSI
-Signal power over the complete 5MHZ carrier which include all components received
-Signal from the current cell and neighboring cells on the same frequency
-Theoretically in an isolated cell having only CPICH power with no other channels
RSSI ≈ CPICH power
-RSSI will change if the carrier use the DCH or the common channels
CPICH Ec/No
-Pilot channel quality ,energy per chip over total received power spectral density
Ec/No= RSCP/RSSI
-The Better this value the better the signal can be distinguished from the over all nosie
-Always negative
-Using Ec/No we can compare different cells
-Using Ec/No handover and cell reselection decisions can be taken
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Noise power spectral density
-Interfering power
-Non interfering power
-Thermal noise
-Test bed being served by single cell
Ec/No of UE is
Measure of PCPICH =RSCP
Measure of total wide band power =RSSI
Assume that UE is in Test bed being served by single cell`
-Cell MAXTXPOWER 20 watt (43 dBm)
-Assuming that 10 % of the cell power is dedicated for CPICH 2 watt (33 dBm)
-If you have no DCH or HS channels
-Ec/No= 10 log (CPICH Power/Total transmitted power)
-Ec/No=10 log (2w/2w)= 10 log 1 = 0
Assume that you start HS session
-Ec/No= 10 log (CPICH Power/Total transmitted power)
-Ec/No=10 log (2w/20w)= -10 dB (Poor value)
-Ec/No will always give a false value for an HSDPA user
CQI Adjustment
Deviating CQI reports lead to faulty decisions
-CQI accuracy will continue to vary depend on :
-UE model
-UE vendor
Deviating CQI
-UE that consistently overestimates the channel quality
+Scheduled too often, at the price of other users.
+Experience a block error rate that is higher than the target 10%, with more retransmissions and reduced system throughput and increased service delay
-UE instead underestimates the channel quality
+Scheduled too seldom.
+Experience a Block error rate will be lower than 10%, which will lead to lower transmitted data rates than possible and hence reduced system throughput.
In both cases, both system throughput and end-user experience of the service is negatively impacted.
To avoid the negative system impact due to inaccurate CQI reports,
-CQI adjustment algorithm
+RBS works on the ACKs and NACKs received from the UE to determine if the UE is overestimating or underestimating the channel quality.
+The algorithm make every effort to achieve a block error rate of 10%
-The output from the adjustment algorithm is CQIadjusted,
-The CQI adjustment algorithm is an optional feature and can be enabled on cell level through parameter cqiAdjustmentOn
